Defrost frozen loaves of gefilte fish, just enough to remove parchment paperPour olive oil into a pan;warm and saute onions for about 5 minutes- removeIn same pan saute mushrooms and peppers for about 5 minutesPreheat oven to 350 degreesCombine all vegetables in pan and add tomato sauce and let simmer 5 minutesPlace both gefilte fish loaves in a square or rectangular glass or ceramic casserole dishPour sauce over loaves and bake covered in oven at 350 for 1 hourLet cool. Then refrigerate overnight.